Hydrogenation of Low Molecular Weight Polymers in Ionic Liquids and the Effects of Added Salt

The biphasic hydrogenations of a number of polymeric materials, polybutadiene (PBD), nitrile-butadiene rubber (NBR) and styrene-butadiene rubber (SBR), were investigated in a toluene/N,N′-butylmethylimidazolium tetrafluoroborate, (BMI+BF4−) system with a water-soluble analogue of Wilkinson's catalyst, RhCl(TPPTS)3 (TPPTS=triphenylphosphine, trisulfonated) at 100 °C and 3.1 MPa. The catalyst shows reasonable activity within ionic liquids with PBD although it was necessary in the case of NBR and SBR to add water as a co-solvent to solubilize the catalyst within the ionic media. Both the extent of hydrogenation and the ratio of the internal 1,4-olefins to vinyl 1,2-olefins were monitored. A clear preference for the external olefins was observed even within NBR and SBR where functionalization on the polymer might enhance the degree of hydrogenation of the internal olefins. The effect of adding NaCl to the PBD system was also investigated. The addition of salt decreases the activity of the catalyst but has no effect on the preference for the hydrogenation of vinyl olefins.